1. Field of the Invention
The present invention generally relates to bicycles, and more specifically to hydraulically-operated control systems for bicycles, particularly shifting systems for bicycles which use a derailleur or similar chain guide to control the position of the drive chain.
2. Description of the Related Art
Typical bicycles can be operated in multiple gears by adjusting a drive chain between a cluster of larger diameter sprockets on the pedal crankshaft and a sprocket cassette mounted on the rear wheel axle. A device known as a derailleur is used to position the drive chain on a given sprocket. Existing mechanical derailleur shifting systems usually incorporate four-bar linkage mechanisms that are controlled by tension cables. A rear derailleur is located on the lower slack side of the drive chain at the rear wheel, and a front derailleur is located on the upper tight side of the chain at the sprocket cluster attached to the pedal crankshaft. The shifting control mechanism for mechanical derailleurs can be mounted on the front down tube of the bicycle frame, but most commonly is mounted on the bicycle handle bars. The shifting control mechanism typically has a small diameter detented or ratcheted pulley around which the derailleur control cable is wrapped. Each derailleur is controlled by its own shifting control mechanism.
So-called xe2x80x9cmountainxe2x80x9d bicycles (designed for off-road use) have become increasingly popular over the past several years, and cyclists are riding these bikes in more harsh environments. Many new innovations have been incorporated into these bicycles to increase their comfort, control, and durability. Elastomeric, air, and hydraulic suspension systems have been added to both the front and rear of mountain bicycles. New hydraulic wheel and disc braking systems have also been introduced. Unfortunately, the front and rear chain shifting systems have remained essentially unchanged; and still use mechanical cables to control the chain guiding mechanisms.
These derailleurs provide satisfactory performance in relatively clean and dry operating environments like those experienced by road bicycles. However, when mountain bikes are used in the dusty, wet, and muddy conditions found on rugged and primitive roads and trails, various contaminants work their way into the derailleur""s pivots and open linkages as well as into and under tension control cables. Such contamination makes the derailleurs difficult to shift, adversely affects their precision in shifting, and also makes them wear out very quickly. The cyclist is thus required to clean, lubricate, adjust and replace mountain bike derailleur components much more frequently. Under extremely harsh operating conditions, existing mechanical derailleurs will fail, making it impossible for the cyclist to change drive ratios.
Products are available which attempt to protect the current design of derailleurs from harsh mountain biking environments. Rubber covers or boots provide some protection for the parallel linkages on the front and rear derailleur mechanisms, but these covers are not waterproof, and mud and water can still enter the mechanisms. New styles of specially coated derailleur control cables are also being offered which are designed to be less affected by mud, water, and dirt. However, dirt can still enter these control cables and cause the cables to stick or bind inside their flexible guide housings.
Alternative derailleur designs exist which do not require tension cables, such as hydraulically-actuated shifting (chain guide) systems. For example, in the design described in U.S. Pat. No. 3,742,777, conventional derailleurs are positioned using sealed actuating bellows which extend within the front or rear derailleur under the influence of hydraulic pressure generated within similar control bellows located in handle bar controller units.
While hydraulic shifting designs may avoid some problems associated with contamination of tension cables and related components, they present several other problems. One significant impediment to the successful commercialization of hydraulic derailleur systems is their size. A hydraulic derailleur that is too large will be more likely to catch on objects (e.g., tree limbs) as the cycle is ridden, and also makes transportation and stowage more difficult (ground and side clearance). The cyclists"" feet might furthermore get caught in a bulky derailleur. Previous hydraulic shifting systems designs are generally larger in size than their mechanical counter parts. This additional size could make these derailleurs more difficult to mount on the bicycle frame as well. Additionally, the larger handle bar mounted actuator units could interfere with the cyclists gripping points on the handle bars, or even reduce knee clearance.
Similarly, the weight of a derailleur system is of great concern to bicycling enthusiasts. Systems which add considerable weight over a cable-tension shifting system will make it more difficult for the cyclist to pedal, particularly uphill. Prior art hydraulic shifting systems designs are again generally heavier than their mechanical pull-cable operated counterparts. In competitive events such as mountain bike races, additional weight on the bicycle frame from heavy shifting components can mean the difference between winning or losing a race.
In light of the foregoing, it would be desirable to devise an improved hydraulic shifting system which avoids the problems associated with mechanical (e.g., cable-pull type) derailleur control devices, and further provides precise and simple operation. It would be further advantageous if the improved hydraulic shifting system could be constructed in a more compact and lightweight design.
It is therefore one object of the present invention to provide an improved hydraulic shifting system for bicycles.
It is another object of the present invention to provide such a hydraulic shifting system that provides precise and simple control in a compact design.
It is yet another object of the present invention to provide such a hydraulic shifting system that is relatively lightweight.
The foregoing objects are achieved in a derailleur device generally comprising a 4-bar linkage, including a housing which acts as one bar of the 4-bar linkage, and three other bars which are located within the housing, as well as means for mounting the housing to a bicycle frame proximate a sprocket cassette and means, located within the housing, for moving the housing relative to the mounting means in response to an actuation force to thereby define a chain guide operating path. The derailleur device may include a detent mechanism formed at least in part on one of the three other bars. In one embodiment, the housing is elongate, and the 4-bar linkage includes a first shaft rotatably attached to the housing at a first end, and a second shaft rotatably attached to the housing at a second end, and the housing rotates around the first shaft in response to the actuation force. The invention is especially directed to a hydraulic implementation wherein the moving means includes a hydraulic assembly which responds to hydraulic pressure exerted by the actuation force. The hydraulic assembly may include a piston which moves within a cylindrical bore, with one of the three other bars of the 4-bar linkage being attached to the piston. The resulting hydraulic derailleur design is comparable to mechanical (cable-pull) derailleurs in size and weight.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.